1. Field of the Invention
This invention relates to fluid circuits for maintaining constant pressure between two abutting solid objects, as for example, a fluid circuit adapted to maintain constant pressure between a compensating roll and a web of flexible material.
2. Description of the Prior Art
Rolls for expanding and contracting flexible materials, such as paper, are known in the art. Such rolls are used for stretching or contracting webs crosswise of their length and for removing wrinkles from moving webs engaged by the rolls. Rolls of the type with which the invention finds utility are curved, or bowed, rolls having a surface of rubber, or the like, mounted on metal segments, generally referred to as spools, or spool assemblies, which are rotatably mounted on a curved axle. Alternatively, the surface may be of metal segments disposed on sections of rubbery material which are rotatable on the curved axle. The opposite ends of the curved axle typically are clamped and are adjustable so that the curved axis of the axle may be set in any selected plane. Such rolls, and the manner of adjustably supporting the rolls, such that the curved axis of the axle thereof may be set in any desired plane, generally function satisfactorily in stretching or contracting webs crosswise of their length, and in removing wrinkles from the webs.
It is found, nevertheless, that in many cases wrinkles in the lengthwise edges of webs are not completely removed because of improper contact with the curved roll. In paper manufacturing, for example, the edges of a web often lengthen more rapidly than the interior body of the web because of differences in temperatures, the physical structure of the paper, and differences in moisture absorption and evaporation. Such often leads to improper edge contact with the curved roll and thus allows wrinkled edges to proceed beyond the curved roll, as illustrated in FIG. 1. In due course, the wrinkled portions of the web must be cut from the web, leading to substantial waste of material.
Recent advances have resulted in tension compensating rolls having end sections which are adjustable to more precisely modify the expansion or contraction of the web along its opposite edges so as to reduce wrinkling of the edges. U.S. Pat. No. 4,692,971, issued Sept. 15, 1987, in the name of James F. Ginter, describes such a compensating roll. The Ginter compensating roll includes a curved axle having a tubular center section and adjustable solid steel end sections. Each of the end sections comprises a shaft fixed to the center tubular section, a hollow tube disposed about the shaft, means on the shaft for pivotally supporting one end of the tube, and means on the shaft for adjustably supporting the other end of the tube to adjust the other end with respect to the shaft.
While the above improvement provides benefits over the prior art, it is necessary that each of the adjustments discussed in the '971 patent be made manually and through trial-and-error. Further, the adjusted positions of the roll must be changed when the web process conditions change.
It would be beneficial to the industry to have a tension compensating roll with end sections which would automatically maintain a substantially constant pressure on the edge areas of a web, and therefore beneficial to have available a fluid circuit which would operate to automatically maintain constant pressure between two abutting solid objects.